1. Field of the Invention
The present invention relates to a sewing machine which forms stitches by controlling operations both of a stitch forming device and of a work fabric feeding device in accordance with a selectively preset mode, and more particularly, to a sewing machine which is capable of releasing a fabric holding pressure according to the mode.
2. Description of the Prior Art
Generally speaking, a sewing machine is equipped with a presser foot for imparting a fabric holding pressure to a work fabric. Each of the sewing machines, which are disclosed, for instance, in the specifications of U.S Pat. Nos. 3,688,714 and 4,538,533 includes a presser foot that is so biased as to move downwards by a spring. When commencing a sewing operation, the above-described presser foot is descended, and the fabric holding pressure corresponding to the biasing force of the spring is applied on the work fabric.
However, since the foregoing presser foot of the sewing machine is disposed at a descending position at which it usually presses the work fabric during the sewing operation, it is unfeasible to automatically release the fabric holding pressure of the presser foot during an automatic sewing operation based on sewing data which are stored beforehand in a storage device.
For this reason, the sewing that will hereinafter be mentioned becomes impractical, this bringing about an inconvenience. To be specific, in order to sew a piece of fabric such as a work fabric having hems which intercross each other to a plain cloth, provided that the sewing data relative to rectilinearity along the hems are stored in the storage device, it is unfeasible for the sewing machine to form circularly arc stitches at a portion where a feeding direction of the fabric is varied while releasing the pressure at this feeding direction varying portion by interrupting the sewing operation on the basis of the sewing data.